Effect of latent heat during primary crystallization on the nanostructural formation process in nanocrystalline soft magnetic materials (original) (raw)
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Nano-crystallisation and magnetic softening in Fe–B binary alloys induced by ultra-rapid heating
Journal of Physics D: Applied Physics, 2018
Magnetically soft nanostructures are known to be prepared by the primary crystallisation of Fe-based amorphous precursors containing Cu and/or Nb. These nonmagnetic additives are essential for accelerated nucleation and retarded crystal growth during crystallisation. However, it has recently been found that none of these additives are necessary for the preparation of similar nanostructures when ultra-rapid annealing (URA) is employed. As a result, a magnetically soft nanostructure with exceptionally high Fe contents is realized in a simple Fe-B binary system. An obvious question is the mechanism of the nanostructural formation in such a simple system. To answer this question, the crystallisation behaviour of amorphous precursors was investigated by means of in situ resistivity measurements with heating rates up to ~100 K s −1. The primary crystallisation temperature (T p) in Fe 86 B 14 is increased at least by ~100 K under URA. This brings T p to the vicinity of the glass transition (T g) predicted by Egami's zeroth-order approximation, suggesting that an enhanced nucleation rate near T g due to the contribution of homogeneous nucleation could be responsible for the nanostructural formation in Fe 86 B 14. Contrarily, the effect of URA is absent from Fe 80 B 14 Nb 6 , and a magnetically soft nanostructure is realized by conventional annealing because the crystallisation reaction in this alloy takes place above T g even with a low heating rate of ~1 K s −1. URA offers new possibilities for enhancing the saturation magnetization in nanocrystalline soft magnetic alloys through reductions of the amount of nonmagnetic additives.
Journal of Alloys and Compounds, 2006
The kinetics of crystallization of a soft magnetic amorphous Fe 40 Ni 38 B 18 Mo 4 alloy was studied by TEM, EDX and resistivity methods. The kinetic parameters were measured from TEM studies and resistivity measurements. Nanocrystals of the fcc FeNi phase were found to crystallize by a primary crystallization mechanism followed by slow growth kinetics. The volume fraction measured by TEM matches well with that calculated from resistivity results and a TTT diagram was constructed. Quantitative measurements of the nucleation and growth rates as a function of temperature and time were performed. The nucleation rate was found to decrease with an increase in heat treatment time due to an increase in boron content in the amorphous matrix as the crystallization took place. The crystal growth was found to slow down considerably due to the presence of Mo. The crystal size was calculated according to the Michels model and compared to our experimental results. Molybdenum was found to dramatically alter the energetics of crystallization, the morphology of the crystals and particularly the kinetics of crystallization. These results offer a method of creating new families of nanostructured magnetic materials by suitable molybdenum addition.
Journal of Bangladesh Academy of Sciences, 2016
To observe the impact of the annealing time on the alloy structure and ultra-soft magnetic properties of Fe 75.5 Si 13.5 Cu 1 Nb 1 B 9 , the alloy was annealed in a controlled way in the temperature range 475-600°C for different annealing time from 5 to 30 min. Amorphosity of the ribbon and nanocrystalline state was evaluated by X-ray diffraction. Grain size and Si content increase with increasing annealing temperature and time; on the other hand lattice parameter decrease with increasing annealing temperature and time. The maximum permeability was observed at annealing temperature Ta = 525°C for 15 min, and thereafter it starts to decreases. Saturation magnetization increases with annealing temperature Ta for the samples and finally decreases during annealing at a temperature much higher than peak crystallization temperature. The results of the experimental observations are explained on the basis of existing theories of nanocrystalline amorphous metallic ribbons.
Scripta Materialia, 2017
The structural and magnetic properties of amorphous Fe 87 − y B 13 Cu y (y = 0 to 1.5) annealed with a range of heating rates (α) up to 150 K/s were investigated. The lowest coercivity (H c) for Fe 87 B 13 after crystallization shows a dramatic decrease from 174 A/m to 6.7 A/m when α is increased from 1.7 K/s to 150 K/s. The coercivity of Fe 87 − y B 13 Cu y annealed at 150 K/s is reduced by Cu addition and H c = 3.0 A/m is obtained at y = 1.5. Nanostructures with a grain size of 15 to 20 nm were evident in transmission electron micrographs from these rapidly annealed alloys.
Effect of crystallization on soft magnetic properties of nanocrystalline Fe80B10Si8Nb1Cu1 alloy
Journal of Magnetism and Magnetic Materials, 2014
The crystallization processes that occur in amorphous melt-spun ribbons of nominal ۱ composition Fe 80 B 10 Si 8 Nb 1 Cu 1 during preparation and heat treatment affect the soft magnetic ۲ properties of this alloy. Fe 80 B 10 Si 8 Nb 1 Cu 1 alloys are prepared by different quenching rates (wheel ۳ speeds of 10, 20 and 40 m/s) and their soft magnetic properties are studied. The XRD data reveal ٤ that as the wheel speed increases, the fraction of crystallinity and the Fe-Si grain size both decrease. ٥ These data also show that the sample prepared by the wheel speed of 10 m/s exhibits α-Fe particles ٦ on its free surface. The data for the samples prepared by the wheel speed of 20 and 40 m/s are in ۷ good agreement with the HRTEM images. VSM measurements show these nanostructured samples ۸ exhibit coercivity in the range of 3 to 21 A/m and magnetic saturation in the range of 1.55 to 1.78 ۹ T.
MRS Proceedings, 2001
Ferromagnetic properties and nanocrystallization process of soft ferromagnetic (Feo.99Moo.ol)78Si9B 1 3 ribbons are studied by transmission electron microscope (TEM), X-ray diffraction (XRD), M6ssbauer spectroscopy (MS), differential scanning calorimeters (DSC) and magnetization measurements. The Curie and crystallization temperature are determined to be Tc=665K and T. = 750K, respectively. The T, value is in well agreement with DSC measurement results. X-ray diffraction patterns had shown a good reconfirm of two metastable phases (Fe2 3 B 6 , Fe 3 B) were formed under in-situ nanocrystallization process. Of which these metastable phases embedded in the amorphous matrix have a significant effect on magnetic ordering. The ultimate nanocrystalline phases of a-Fe (Mo, Si) and FeB at optimum annealing temperature had been observed respectively. It is notable that the magnetization of the amorphous phase decreases more rapidly with increasing temperature than those of nanocrystalline ferromagnetism, suggesting the presence of the distribution of exchange interaction in the amorphous phase or high metalloid contents.
Thermal effect on structural and magnetic properties of Fe78B13Si9 annealed amorphous ribbons
EPJ Web of Conferences
In the present work, we study the influence of thermal treatments on the magnetic properties of as-quenched and pre-crystallized Fe 78 Si 9 B 13 after stress relaxation. The crystallization behavior of amorphous and treated Fe 78 Si 9 B 13 ribbons was revisited. The measurements were carried out by means of Differential Scanning Calorimetry, by X-ray diffraction and by Vibrating Sample Magnetometer, Susceptometer and fluxmeter. Relaxed samples were heated in the resistivity device up to 700°C and annealed near the onset temperature about 420°C for respectively 1, 3, 5, 8 hours. In asquenched samples, two transition points occur at about 505°C and 564°C but in relaxed sample, the transition points have been found about 552°C and 568°C. Kinetics of crystallization was deduced for all studied samples. Annealing of the as-purchased ribbon shows the occurrence of Į-Fe and tetragonal Fe 3 B resulting from the crystallization of the remaining amorphous phase. The effects on magnetic properties were pointed out by relating the structural evolution of the samples. The magnetic measurements show that annealing change the saturation magnetization and the coercive magnetic field values, hence destroying the good magnetic properties of the material. The heat treatment shows that the crystallization has greatly altered the shape of the cycles and moved the magnetic saturation point of the samples. The effect of treatment on the magneto-crystalline anisotropy is also demonstrated.
Magnetism of Nanocrystallized Amorphous Fe75B10Si15
2012
Amorphous ribbons of alloy composition Fe 75 B 10 Si 15 are cast by melt spinning and annealed to partially nanocrystalline states. The magnetic properties are investigated by VSM and MTGA. Structure is examined using XRD and SEM. Results obtained show nanostructured material with excellent soft magnetism in samples annealed at temperatures below the crystallization temperature as well as enhancement of magnetic hardness for annealing at high temperatures. This validates Herzer's Random Anisotropy model of magnetism in nanostructured materials and provides basis for further inquiry into tweaking alloy compositions and/or manipulating annealing parameters. Also, increase of Curie temperature is noted with respect to increasing annealing temperatures arising from stress relaxation, validating a study on the relationship between the two.
Fe-Co-B Soft Magnetic Ribbons: Crystallization Process, Microstructure and Coercivity
Materials, 2020
In this work, a detailed microstructural investigation of as-melt-spun and heat-treated Fe67Co20B13 ribbons was performed. The as-melt-spun ribbon was predominantly amorphous at room temperature. Subsequent heating demonstrated an amorphous to crystalline α-(Fe,Co) phase transition at 403 °C. In situ transmission electron microscopy observations, carried out at the temperature range of 25–500 °C and with the heating rate of 200 °C/min, showed that the first crystallized nuclei appeared at a temperature close to 370 °C. With a further increase of temperature, the volume of α-(Fe,Co) crystallites considerably increased. Moreover, the results showed that a heating rate of 200 °C/min provides for a fine and homogenous microstructure with the α-(Fe,Co) crystallites size three times smaller than when the ribbon is heated at 20 °C/min. The next step of this research concerned the influence of both the annealing time and temperature on the microstructure and coercivity of the ribbons. It wa...
Journal of Bangladesh Academy of Sciences, 1970
Structural and magnetic measurements have been performed on the FINEMET type of ribbons with nominal composition of Fe 74 Cu 0.5 Nb 3 Si 13.5 B 9 synthesized by rapid solidification technique. The crystallization behavior and the nanocrystal formation have been studied by differential thermal analysis (DTA) and X-ray diffraction (XRD). The crystallization onset temperatures determined by XRD are in good agreement with DTA results. Magnetic permeability and magnetization measurements have been carried out using inductance analyzer and vibrating sample magnetometer (VSM). Magnetic permeability sensitively depends on the annealing temperature which increases sharply with the increase of annealing temperature. Maximum permeability corresponding to optimum annealing temperature (T a) was observed at T a = 575°C. Saturation magnetization, M s, increases with T a for the sample and finally decreases for annealing at a temperature much higher than peak crystallization temperature. The results show that the amounts of Cu and Nb are very important for the soft magnetic properties of FINEMET alloys.